Optical colored films have important uses, for example as optical filters or optical protection films, and as window films for automobile, domestic and office windows for adjusting sunlight irradiation in the energy-saving fields. The high-end optical colored films available currently are generally obtained by vacuum evaporation or plasma sputtering which has high cost and furthermore is only suitable for preparation of small-size samples due to limitation of the vacuum cavity and the size of target material.
The substrates of the optical colored films are generally polyester films. Large-scale industrial preparation of the optical colored films generally adopts the following techniques:
One known preparation method of a colored film relies upon adding a colorant into molten mass of polyester raw material and directly obtaining a colored film by blow molding through an extruder. The colored film obtained using the method has excellent performance, but this process is unrealistic for dyeing few films and is inconvenient for preparation of films needing frequently changing colors. Meanwhile, the transparence and grey of the film have certain defects.
Another known polyester film dyeing methods comprise a solvent method and a solvent-assisted method. The solvent method dyes a polyester film in organic solvent dissolved with a disperse dye, and the organic solvent acts as the dissolution medium of disperse dye and simultaneously has the swelling action on the polyester films so as to facilitate dye molecules to disperse inside the film. The solvent-assisted method utilizes a suspension of disperse dye in water phase to dye a film using the suspension around the boiling point of water by adding an appropriate organic solvent. Both the methods need processing around the boiling points of water phase and the solvent, have high solvent loss, need long time, and may not guarantee uniform dyeing of the films. Especially, long time results in great increase of cost, thereby being unfavorable for industrial production.
The Chinese patent No. CN1243133 discloses another method for preparing a colored film in which a disperse dye, a thickener and water are mixed to obtain a dye mixture with certain viscosity, followed by roller coating on a surface of a polyester film which is heated to enable the dye to thermally migrate into the film from the coating layer, and finally unwanted dye and water soluble thickener on the surface of the film are removed by alternating rinsing with solvent or cold and hot water to obtain the colored polyester film. The preparation method only can obtain the polyester film with one colored side, and dyeing two sides needs repeating the same process, thereby being cumbersome and inconvenient. In addition, uniform roller coating is a technical problem under optical grade requirement.